My specific goal is setting
'vc-mode from the $PROMPT1 snippet so that the mode line will show useful VC info in shell-mode.
I can use
emacsclient -e '(setq vc-mode "foo")' but that's not quite enough since
'vc-mode needs to be a buffer local variable, and so I will first need to pass the name of the
shell-mode buffer into bash somehow.
Is there a known pattern for doing this kind of thing?